Model Test Of Artificial Freezing Temperature Field In High Velocity Permeable Formation

The freezing method is currently the main construction method for shaft excavation and construction of water-rich soft soil layers.The existence of groundwater flow affects the success of the project,based on the saturated porous media as the research object,By accurately controlling the velocity and direction of the seepage field,and fully considering the influence of the boundary conditions of the water and heat fields,a large-scale water-heat coupling physical model test system was constructed.application of the system on the velocity of percolation formation space-time evolution regularity of single pipe freezing temperature field were studied,At the same time,the experimental results are analyzed based on the characteristics of heat conduction and convective heat transfer.The results show that:when the seepage velocity v=3m/d,the temperature drop rate of the freezing temperature field decreases,but the difference between the final shape and the extended range of the freezing front and the state of no flow velocity is small after entering the stable freezing stage.When the seepage velocity v=6m/d and 9m/d,the temperature drop rate of the frozen area further decreases,and the temperature of the upstream area is significantly higher than that of the downstream area.After continuous freezing for 24 hours,the freezing front extends to the upstream/lateral/downstream area,and then decreases by 72.27%/52.83/27.73%and 76.89%/55.89%/39.07%respectively when there is no flow velocity.The rationality of the mathematical model is verified by the combination of similar model test and numerical simulation.On the basis of the mathematical model,combined with the design parameters of the freezing scheme in a mining area in huainan,the optimization effects of the seven optimization schemes are analyzed by numerical calculation.Results show that under the action of groundwater flow velocity is larger,the frozen pipe arrangement around the upper position of the freeze effect is affecting the whole frozen wall in circle time and the thickness of the decisive factor,after the location of the encryption processing of freeze pipe upstream,narrowing the spacing between adjacent frozen pipe,increasing the supply the cold upper area,so as to shorten the upstream area of the frozen wall of lap time,thus improve the efficiency of the freezing of the whole of the frozen wall.When the encryption Angle is 105 and the distance between the freezing pipes is reduced to lm,the maximum flow rate of the freezing cross circle reaches 13m/d,which is 62.5%higher than that before the optimization(8m/d).Moreover,the thickness of the freezing wall formed by the optimized freezing scheme is significantly greater than that before the optimization due to the same freezing time.This study will provide a reliable basis for the development of numerical calculation and theoretical analysis,and an important reference for the layout spacing of freezing pipes in large velocity permeable formations.Figure65 Table11 References84...